arm64: module: remove old !KASAN_VMALLOC logic

Historically, KASAN could be selected with or without KASAN_VMALLOC, and
we had to be very careful where to place modules when KASAN_VMALLOC was
not selected.

However, since commit:

  f6f37d9 ("arm64: select KASAN_VMALLOC for SW/HW_TAGS modes")

Selecting CONFIG_KASAN on arm64 will also select CONFIG_KASAN_VMALLOC,
and so the logic for handling CONFIG_KASAN without CONFIG_KASAN_VMALLOC
is redundant and can be removed.

Note: the "kasan.vmalloc={on,off}" option which only exists for HW_TAGS
changes whether the vmalloc region is given non-match-all tags, and does
not affect the page table manipulation code.

The VM_DEFER_KMEMLEAK flag was only necessary for !CONFIG_KASAN_VMALLOC
as described in its introduction in commit:

  60115fa ("mm: defer kmemleak object creation of module_alloc()")

... and therefore it can also be removed.

Remove the redundant logic for !CONFIG_KASAN_VMALLOC. At the same time,
add the missing braces around the multi-line conditional block in
arch/arm64/kernel/module.c.

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Will Deacon <will@kernel.org>
Tested-by: Shanker Donthineni <sdonthineni@nvidia.com>
Link: https://lore.kernel.org/r/20230530110328.2213762-2-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: mrutland-arm

arch/arm64/kernel/kaslr.c

@@ -48,16 +48,6 @@ static int __init kaslr_init(void)
 
 	pr_info("KASLR enabled\n");
 
-	/*
-	 * KASAN without KASAN_VMALLOC does not expect the module region to
-	 * intersect the vmalloc region, since shadow memory is allocated for
-	 * each module at load time, whereas the vmalloc region will already be
-	 * shadowed by KASAN zero pages.
-	 */
-	BUILD_BUG_ON((IS_ENABLED(CONFIG_KASAN_GENERIC) ||
-	              IS_ENABLED(CONFIG_KASAN_SW_TAGS)) &&
-		     !IS_ENABLED(CONFIG_KASAN_VMALLOC));
-
 	seed = get_random_u32();
 
 	if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {

arch/arm64/kernel/module.c

@@ -32,33 +32,16 @@ void *module_alloc(unsigned long size)
 	if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
 		gfp_mask |= __GFP_NOWARN;
 
-	if (IS_ENABLED(CONFIG_KASAN_GENERIC) ||
-	    IS_ENABLED(CONFIG_KASAN_SW_TAGS))
-		/* don't exceed the static module region - see below */
-		module_alloc_end = MODULES_END;
-
 	p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
-				module_alloc_end, gfp_mask, PAGE_KERNEL, VM_DEFER_KMEMLEAK,
+				module_alloc_end, gfp_mask, PAGE_KERNEL, 0,
 				NUMA_NO_NODE, __builtin_return_address(0));
 
-	if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
-	    (IS_ENABLED(CONFIG_KASAN_VMALLOC) ||
-	     (!IS_ENABLED(CONFIG_KASAN_GENERIC) &&
-	      !IS_ENABLED(CONFIG_KASAN_SW_TAGS))))
-		/*
-		 * KASAN without KASAN_VMALLOC can only deal with module
-		 * allocations being served from the reserved module region,
-		 * since the remainder of the vmalloc region is already
-		 * backed by zero shadow pages, and punching holes into it
-		 * is non-trivial. Since the module region is not randomized
-		 * when KASAN is enabled without KASAN_VMALLOC, it is even
-		 * less likely that the module region gets exhausted, so we
-		 * can simply omit this fallback in that case.
-		 */
+	if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS)) {
 		p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
 				module_alloc_base + SZ_2G, GFP_KERNEL,
 				PAGE_KERNEL, 0, NUMA_NO_NODE,
 				__builtin_return_address(0));
+	}
 
 	if (p && (kasan_alloc_module_shadow(p, size, gfp_mask) < 0)) {
 		vfree(p);